|Japanese Name:||相生 祐子|
|Romanized Name:||Aioi Yūko|
|English Name:||Yuuko Aioi|
|First Appearance:||"Nichijou Episode 0"|
|Affiliated:|| Mio Naganohara (friend)|
Mai Minakami (friend)
Nano Shinonome (friend)
Mother Aioi (mother)
|Japanese VA:||Mariko Honda|
Yuuko Aioi is an energetic high school girl with short brown hair. She's the one of Aioi Household family. Usually Mio, Mai, and Hakase call her by her nickname, Yukko (ゆっこ).
Yuuko Aioi is fair-skinned and has short pale chestnut brown hair with bangs pointed in the middle. Her other part of the bangs which appear on the outer sides are shorter and pointed. Her ends are pointed outwards and has short strands that reach to the middle of her ears. She has dark umber brown eyes and wears her girl's school uniform.
Her school uniform consists a pale beige sailor top-like blazer with thin white stripes in the middle and at the end of the blazer with a curved white sailor collar that has a thick pale red stripe nearly around the edges and short pale red bow with a chest pocket at the right side. Her top inner part of her sailor top also has a thick pale red stripe nearly around the edges and has white cuffs at the end of her sleeves. She wears a pale red skirt and has darker red pleated designs on it. She wears it with white knee socks and dark greyish- brown tassel loafers with white soles.
She also wears another one of her girl's school uniform consisting white dress-shirt like-sailor top with short sleeves. It has a flat collar with a thick light blue stripe nearly reaching around the edges and wears a short light blue tie. Her sleeves have thick light blue stripes at the top. Her back of her collar is long and curved. She wears it with a navy blue skirt, white knee socks, and white uwabaki slippers with darker blue tips. She sometimes wears tassel loafers with it.
In her character arts, she is shown wearing casual outfits.
In her home, she wears a short-sleeved V-neck white T-shirt with a hot pink T-shirt with short sleeves which are slightly longer.
Mio Naganohara is Yuuko's closest friend, but they are opposites in almost every way. This causes some tensions between them at times, but they usually appreciate each other's company. Even though Mio tends to be forgiving with her, some of Yuuko's actions occasionally (almost always unintentionally) lead her to furious outbursts. Yuuko, on the other hand, is often prone to cheer up Mio and/or praise her for her qualities when the time comes. Mio sits in front of Yuuko in class.
Yuuko has known Mai since middle school, after the latter moved to Japan from Alaska. Whenever Yuuko tries to make Mai laugh, Mai responds nonchalantly. This causes Yuuko to try to make up for humor deficiencies, though to continued failure. Mai in return has a habit of frequently teasing Yuuko though silent but outrageous actions, knowing full well Yuuko cannot react appropriately.
Nano is quite close to Yuuko, despite the fact that the latter is not very smart. Yuuko's imagination was originally the only thing that led her to believe she was a robot because of the wind-up key on her back, but Yuuko only liked Nano more because of it. Indeed, she finds the fact that Nano is a robot to be amazing. Although she knows that Nano is a robot, she never tells anybody about it. Like Mio, Nano is frequently exasperated by Yuuko's eccentricies, though she attempts to reason with her unlike Mio and Mai.
Thanks to her easygoing personality, love for robots and "cool things" in general, Yuuko and Hakase became friends almost instantly after she entered the Shinonome Laboratory. Hakase is always ecstatic when Yuuko comes to visit, and will often fight to ensure she does not leave.
- Mother Aioi : Yuuko's mother. Her strict attitude often results in Yuuko being physically disciplined for acting up or her poor grades.
- Buddy : A dog who frequently appears to comfort Yuuko in times of crisis.
- Yuuko is constantly persecuted by bad luck regardless of whether or not her laziness was a factor. This trait is occasionally emphasized by the appearance of a mysterious dog which puts his paw on her back trying to comfort her after an unfortunate event.
- Yuuko's "classroom dream" (which is some sort of mini-story that Yuuko dreams about when she falls asleep during classes) is the premise of the Nichijou PSP video-game.
- In moments of depression, Yuuko comes up with poems relating to her present situation. This typically results from being forced into the hallway for disrupting the class.
- When she was in elementary school, Yuuko wanted to be a frilled-neck lizard.
- Yuuko's name means "blessed child", with 祐 (yuu) meaning "divine aid; divine grace" and 子 (ko) meaning "child." It also may be a pun on 悠 (yuu) which means "leisurely."
- Yuuko is a 16 year old Capricorn. Her blood type is A-.
- Yuuko owns a cat named Chissan.
- In the manga, Yuuko is one of the few people aware of Sakamoto's ability to speak thanks to Hakase's scarf, something which still never fails to amaze her.
- She's precisely 48 cm taller than Hakase.
- Yuuko is the only one in Trio Sucharaka whose name does not start with M. She is also the most tomboyish of the three.
- "Super Ultra Great Delicious Wonderful Bad"
- "Just kidding" (なんちゃって - nanchatte)
- Nichijou Character Song 5 - Aioi Yuuko - released Aug 10, 2011.
- WEB Radio - Nichijou no Radio - the theme of the radio program "Nichijou no Radio" - released Jul 6, 2011.
- "Yukko-Mio-Mai no Sucharaka San-nin Shuu" - with Mio and Mai
- Nichijou no Gasshou Kyoku - a collection of outro theme starting from episode 14 - released Oct 5, 2011.